How to share an internet connection in OS X

Share your Mac's broadband with a few clicks

Shares

Getting your Mac online is generally quite straightforward, especially if you run your own AirPort network or connect through a USB or Ethernet cable directly to a router or cable modem.

Troubleshooting connection issues can often be as simple as restarting a router, modem or Mac. This doesn't always work, of course. The culprit could be an older Mac or an outdated version of Mac OS X.

Occasionally, a Mac may refuse to see the network even though it's set up correctly. A more common occurrence, however, involves having an older Mac that desperately needs updating – but lacks a wireless card.

Making connections

Increasingly, homes and offices have wireless networks, which means plugging a problematic Mac directly into the router can be a fiddly process and not a practical solution. An ideal workaround would be to get the Mac online without connecting it to a router.

What you may not know is that OS X has for some time offered the ability to share a Mac's internet connection to other computers across a variety of connection formats. The Sharing tab in System Preferences is home to an option to turn on Internet Sharing.

With this, you can choose a source, which is the means by which the Mac connects to the internet, and a destination – the method or device through which you want to connect the second Mac. The available options vary depending on your model and the selected options.

Almost all Macs have a FireWire port, so this should appear as an optional destination. Should your Mac have Bluetooth – which has been enabled in its System Preferences pane – this should also appear.

A typical example is to share a Mac's Ethernet broadband connection over FireWire using this setup window, and then plug a FireWire cable between the two Macs. OS X will then 'broadcast' the broadband connection across the cable to the second Mac and, in most cases, it should be able to see it, with a reboot of the second Mac occasionally necessary to enable the connection to be identified properly.

If this doesn't work, you can go into the network preferences on the second Mac – which will vary slightly depending on the version of OS X it's running – and select the network interface's properties to make sure it's working.

Sometimes you might have to manually add or activate a port – especially FireWire – to bring it online. The same applies to sharing a Mac's AirPort connection over Bluetooth or Ethernet.

AirPort wireless

You can also set up your own wireless network without the need for a router, as long as you have an AirPort card-equipped Mac connected directly to the internet. If you choose to share its AirPort connection to other AirPort Macs by selecting Create Network from the AirPort icon in the menu bar, you can effectively create a wireless network, complete with password protection.

How to share your Mac's internet connection

1. Choose a source

Go to System Preferences > Sharing and locate the Internet Sharing option. Don't activate it yet, otherwise you won't be able to change its settings. In almost all circumstances, your Mac's internet will be coming via AirPort or Ethernet. Choose either of these as the source in the menu with the Share your connection from: prefix.

2. Choose a destination

Decide which port you want to use to share the connection. Let's say it's FireWire – choose this from the To computers using: list. Then tick the box next to Internet Sharing in the Service list on the left to start it up.

Connect the second Mac to the first by plugging a FireWire cable between them. The second Mac may need a restart and you may have to go into its Network pane in System Preferences to add FireWire as a network location.

Some versions of OS X will automatically detect all available interfaces, but occasionally you have to add them manually. You can connect the two Macs using an Ethernet cable by selecting the appropriate option.

If you choose to share an Ethernet connection over Ethernet, which is technically possible, OS X warns you that this has the potential to cause conflicts with your ISP. If you want to take this approach it's worth checking with them.

3. Set up Bluetooth

Perhaps you want to share an Ethernet connection over Bluetooth. Go to System Preferences > Hardware > Bluetooth and click Advanced. From here you can activate an option called Share my internet connection with other Bluetooth devices.

If you check this box and return to the internet sharing section, you'll see that Bluetooth appears as both an available source and destination.

4. Share an AirPort connection

Consider this scenario: you have a Mac connected to the internet via a direct cable or USB modem. This is quite common, especially with iMacs or tower Macs such as G4s, G5s or Mac Pros. If that Mac also happens to have an AirPort card installed, it might not be in use since the Mac sits next to the modem, so you don't need a wireless network.

But if you have an iPod touch, iPhone or laptop, you really want to be able to get online wirelessly as well. Normally you would have to buy an AirPort base station or third-party wireless router to achieve this, but you may not have known that you can use the AirPort card in the Mac as a base station.

Making sure the AirPort card is enabled in the Network pane of System Preferences, click on its icon in the menu bar and choose Create Network.

Alternatively, in the Internet Sharing pane, choose Ethernet from the source list and activate AirPort as a destination, then click the AirPort Options button. Both methods bring up the Create Network window.

5. Protect your network

In the Create Network window, choose a name for the wireless network, which will be broadcast from the Mac. Then choose a wireless channel, which can usually safely be left on Automatic (11).

Check the box to require a password, then choose a 40 or 128-bit WEP key as a security option and select a password. Use a five character password for a 40-bit key and a 13-character password for a 128-bit key, the latter being more secure.

6. Join the new network

From the other Mac, Windows laptop, iPod touch or iPhone, choose to join the new network, which should appear as an available network. The AirPort icon in the menu bar of the net-connected Mac will display a tiny arrow icon to denote that its connection is being shared.

So now you are sharing your Ethernet or USB internet connection to wireless clients securely, and all without having to purchase any extra hardware!

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